Bohol island, Philippines Earthquake: Crustal deformation detected by satellite SAR data

A Mw7.1 (USGS) (Mw7.2: PHIVOLCS) earthquake occurred in Bohol island, Philippines on October 15, 2013. Applying an elaborated SAR image analysis (pixel offset method) using RADARSAT-2 data operated by Canadian Space Agency (CSA), we have successfully grasped the whole picture of the crustal deformation associated with the earthquake.

• An intensive deformation extends in the northwestern area of the island with ground displacement exceeding 1 m.
• The crustal deformation zone appears with the length of approximately 50 km in the ENE-WSW direction.
• The ground in the southern side of the crustal deformation area (red-colored area) moves toward the satellite (uplift / westward movement), while in the northern side the ground moves away from the satellite (subsidence / eastward movement).
• A clear displacement discontinuity with the length of about 5 km, across which the ground movement is in the opposite direction, can be identified in the northeastern part. There are several reports that the surface fault ruptures appear near the displacement boundary.
• The observed crustal deformation pattern is consistent with that produced by a reverse fault motion on a south-southeast dipping fault plane.
• Shoreline changes are detected around from Maribojoc to Loon by an additive color process using SAR amplitude images, suggesting that the ground uplifted and the shoreline shifted seaward resultantly.

 NOTE: This is a preliminary result. The result is possibly updated with further elaborated analyses.
 
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Figure 1.
Red and blue-colored areas represent displacements toward and away from the satellite, respectively, which can be explained by uplift/westward movement and subsidence/eastward movement, respectively. The satellite used in this analysis illuminates microwave obliquely downward from the western sky.
 
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Figure 2.
The left panel shows an enlarged view of the northeastern area (white frame of Figure 1). The right panels show displacement changes along the cross sections of A-B and C-D shown in Figure 1. A sharp large displacement change can be seen in the A-B cross section, suggesting a displacement offset due to the surface rupture.
 
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Figure 3. Shoreline changes derived by an additive color process
Red- and cyan-colored areas represent emergence and submergence of the land (increase and decrease of the backscatter intensity), respectively.

Date Time	15 October, 2013 00:12 (UTC)
Hypocenter Location	9.877°N, 124.118°E Depth: 20.7km (USGS) 9.86 °N, 124.07°E Depth: 12km (PHIVOLCS)
Magnitude	Mw=7.1 (USGS), Mw=7.2 (PHIVOLCS)

RADARSAT-2（CSA: Canadian Space Agency）

KOBAYASHI Tomokazu: Researcher
TOBITA Mikio: Principal Researcher